The paper deals with the problem of the determination of the effects of temperature on the efficiency of the nitrification process of industrial wastewater, as well as its toxicity to the test organisms. The study on nitrification efficiency was performed using wastewater from one of Polish chemical factories. The chemical factory produces nitrogen fertilizers and various chemicals. The investigated wastewater was taken from the influent to the industrial mechanical-biological wastewater treatment plant (WWTP). The WWTP guaranteed high removal efficiency of organic compounds defined as chemical oxygen demand (COD) but periodical failure of nitrification performance was noted in last years of the WWTP operation. The research aim was to establish the cause of recurring failures of nitrification process in the above mentioned WWTP. The tested wastewater was not acutely toxic to activated sludge microorganisms. However, the wastewater was genotoxic to activated sludge microorganisms and the genotoxicity was greater in winter than in spring time. Analysis of almost 3 years’ period of the WWTP operation data and laboratory batch tests showed that activated sludge from the WWTP under study is very sensitive to temperature changes and the nitrification efficiency collapses rapidly under 16°C. Additionally, it was calculated that in order to provide the stable nitrification, in winter period the sludge age (SRT) in the WWTP should be higher than 35 days.
In the study the comparative analysis of test results of drainage of municipal wastewater sludge was conducted with the use of flocculant Praestol 855BS and the mixture of flocculant Praestol 855BS 50% + orange essential oil 50%, as the reagents supporting this process. It was also attempted to reduce unpleasant smells exuding from the drained sludge.
The process of drainage of municipal wastewater sludge was conducted in the laboratory setting centrifuge of MPW-350 type. The variable independent parameters were centrifugation time, centrifugation speed, dosage of flocculant Praestol 855BS as well as dosage of mixture in the proportion of flocculant Praestol 855BS (50%) + orange essential oil (50%). The following parameters were subject to assessment: water content in the sludge, dry mass content in the reflux as well as time of maintenance of the oil’s smell in the sludge. The conducted tests demonstrated that the orange essential oil has an impact on drop in resultant quality parameters of the drainage process of municipal wastewater sludge. Batching of the orange essential oil has an impact on considerable reduction of odours exuding from drained wastewater sludge, and thus on improvement of work conditions connected with operation of centrifugal separators. Bearing in mind both the efficient drainage process of wastewater sludge as well as simultaneous reduction of unpleasant smells exuding from the sludge during this process it is assumed and recommended to simultaneously apply both reagents, that is flocculant Praestol 855BS (50%) and orange essential oil, also in the volume of 50%.
Ultrasonic disintegration, as a method of sludge pre-treatment (before the stabilization process), causes changes in their physicochemical characteristics. The aim of this study was to determine the influence of ultrasonic disintegration conditions (sonication) on the changes in the physicochemical characteristics of sonicated sludge, i.e. an increase in the content of organic substances in the supernatant, sludge dewaterability and flocs structure. Thickened and non-thickened excess sludge from the municipal wastewater treatment plant in Gliwice was disintegrated. The process was conducted, using a high-power disintegrator equipped with a lenticular horn. In order to determine the most favorable conditions, the sewage sludge was sonicated at a wave frequency of f=25 kHz (as a function of time), with a different samples volume (V1=0.5 and V2=1 L) and emitter position of 1 and the 2.5 cm from the bottom of the chamber in which the process was conducted. The disintegration of sewage sludge was carried out with a specific energy density (EV) in the range from 10 to 30 kWh/m3. The evaluation of the disintegration effects was based on changes in the physicochemical characteristics of the sludge and/or supernatant at the end of the process, expressed by commonly used and author’s disintegration indicators. The best results were obtained for the sludge disintegrated with a volume of V2=1 L and the emitter position of 2.5 cm from the bottom of the chamber. The study confirms that in various operating conditions of ultrasonic disintegration, there is a possibility for obtaining different effects which may influence the course of anaerobic stabilization and quality of the final products of the process.